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#include "os.h"
#include <mp.h>
#include "dat.h"
// convert an mpint into a big endian byte array (most significant byte first)
// return number of bytes converted
// if p == nil, allocate and result array
int
mptobe(mpint *b, uchar *p, uint n, uchar **pp)
{
int i, j, suppress;
mpdigit x;
uchar *e, *s, c;
if(p == nil){
n = (b->top+1)*Dbytes;
p = malloc(n);
}
if(p == nil)
return -1;
if(pp != nil)
*pp = p;
memset(p, 0, n);
// special case 0
if(b->top == 0){
if(n < 1)
return -1;
else
return 1;
}
s = p;
e = s+n;
suppress = 1;
for(i = b->top-1; i >= 0; i--){
x = b->p[i];
for(j = Dbits-8; j >= 0; j -= 8){
c = x>>j;
if(c == 0 && suppress)
continue;
if(p >= e)
return -1;
*p++ = c;
suppress = 0;
}
}
// guarantee at least one byte
if(s == p){
if(p >= e)
return -1;
*p++ = 0;
}
return p - s;
}
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